The present invention relates to piston rings and particularly to compression rings suitable for applying to internal combustion engines.
Recently, high efficiency has become more and more desirable for internal combustion engines. In addition, it has become necessary to consider the treatment of exhaust gas. Thus, great consideration has been given to the problems caused by increases in fuel costs and the lowering of power of internal combustion engines. With respect to these problems, compression rings for keeping the combustion chamber of the internal combustion engine airtight have a large influence upon the efficiency of the internal combustion engines. It has thus become necessary to consider the characteristics of such compression rings.
Heretofore, cast iron rings or oil temper wires composed of carbon steel or silicon-chromium steel have been used as compression rings for internal combustion engines. In the cast iron rings, however, it is difficult to produce rings which are thin in the axis direction. Because of poor strength at a high temperature in the silicon-chromium rings, it is necessary that the cross-sectional area be relatively large, and thus the weight becomes large. Therefore, they have disadvantages that the inertia is large and a fluttering phenomenon (extraordinary vibration of rings) which causes leakage of fuel gas easily occurs. Furthermore, with respect to both the cast iron rings and the silicon-chromium rings, since heat collapse resistance and wear resistance in upper and lower sides, i.e., sides perpendicular with respect to the axial direction are insufficient, it is impossible to fit the ring on a position near the top of the piston so as to be advantageous for a countermeasure for exhaust gas, and that, since the interval between the rings cannot be shortened, the weight of the piston increases and high efficiency cannot be attained.